Same problem here on another asset not related to landmass,
UATHelper: Packaging (Windows): LogCook: Error: Content is missing from cook. Source package referenced an object in target package but the object was stripped out of the target package when saved.
UATHelper: Packaging (Windows): Source package: /Game/A_DarkEvil/Maps/WP/L_DarkEvill_WP_OK/Generated/7JC11A382LKLD2L2RX43207AC
UATHelper: Packaging (Windows): Target package: /AscentCombatFramework/Blueprints/AI/AIs/ACFAICharacterBP
UATHelper: Packaging (Windows): Referenced object: /AscentCombatFramework/Blueprints/AI/AIs/ACFAICharacterBP.ACFAICharacterBP_C:ACF Effects Manager Comp_GEN_VARIABLE